42 research outputs found
Tunable Backward Terahertz-wave Parametric Oscillation
Backward optical parametric oscillation has attracted attention for cavityless spectral narrowband generation based on perfect photon conversion. Few demonstrations have shown its potential from the aspect of nonlinear photonics; therefore, the mechanisms of momentum conservation among interacting light waves have been concealed by the restricted configuration under the phase-matching condition of periodically poled structures. Here, we unveil a tunable mechanism in the terahertz region by active control of the phase-matching condition. The tunability of backward terahertz-wave parametric oscillation is investigated using a quasi-collinear phase-matching model and its frequency range from the sub-terahertz to terahertz region is identified. Transform-limited terahertz-wave pulse is achieved simply by installing a device on the pump propagating line with no cavity. Moreover, the cascading terahertz-wave generation enhances the photon conversion efficiency, thus making nonlinear optics and its applications more promising. The results highlight new capabilities for using modern ferroelectric materials and encourage further research on nonlinear optics
Incident-Angle-Dependent Extraordinary Transmission of the Terahertz Bull’s-Eye Structure
The bull’s-eye structure in the terahertz (THz) frequency region has ample applications owing to its ability to focus free-propagating waves into subwavelength apertures, resulting in enhanced transmission, that is, extraordinary transmission. However, its coupling properties have been primarily discussed in terms of the normal plane-wave incidence to the structure. In this study, we investigate the multiple resonances in extraordinary transmission with normal and oblique incident waves. The experiment using a widely tunable and high-power THz wave source revealed two types of resonances. The main resonance split depends on the incident angle, and the other corresponds to the side lobe of the main resonances. The results are explained by a simple analytical model using a finite number of scattering media. The analysis is supported by the full-wave simulation using the finite-element method, which agrees with the experimental results. The coupling mechanisms will be applicable to design devices, such as THz biosensing devices or THz antennas for rapid communication systems
Nanometer-precision surface metrology of millimeter-size stepped objects using full-cascade-linked synthetic-wavelength digital holography using a line-by-line full-mode-extracted optical frequency comb
Digital holography (DH) is a powerful tool for surface profilometry of
objects with sub-wavelength precision. In this article, we demonstrate
full-cascade-linked synthetic-wavelength DH (FCL-SW-DH) for nanometer-precision
surface metrology of millimeter-size stepped objects. 300 modes of optical
frequency comb (OFC) with different wavelengths are sequentially extracted at a
step of mode spacing from a 10GHz-spacing, 3.72THz-spanning electro-optic
modulator OFC (EOM-OFC). The resulting 299 synthetic wavelengths and a single
optical wavelength are used to generate a fine-step wide-range cascade link
covering within a wavelength range of 1.54 um to 29.7 mm. We determine the
0.1000mm-stepped surface with axial uncertainty of 6.1 nm within the maximum
axial range of 14.85 mm.Comment: 22 pages, 6 figure
Low phase noise THz generation from a fiber-referenced Kerr microresonator soliton comb
THz oscillators generated via frequency-multiplication of microwaves are facing difficulty in achieving low phase noise. Photonics-based techniques, in which optical two tones are translated to a THz wave through opto-electronic conversion, are promising if the relative phase noise between the two tones is well suppressed. Here, a THz (≈560 GHz) wave with a low phase noise is provided by a frequency-stabilized, dissipative Kerr microresonator soliton comb. The repetition frequency of the comb is stabilized to a long fiber in a two-wavelength delayed self-heterodyne interferometer, significantly reducing the phase noise of the THz wave. A measurement technique to characterize the phase noise of the THz wave beyond the limit of a frequency-multiplied microwave is also demonstrated, showing the superior phase noise of the THz wave to any other photonic THz oscillators (>300 GHz)
Low phase noise THz generation from a fiber-referenced Kerr microresonator soliton comb
THz oscillators generated via frequency-multiplication of microwaves are
facing difficulty in achieving low phase noise. Photonics-based techniques, in
which optical two tones are translated to a THz wave through opto-electronic
conversion, are promising if the relative phase noise between the two tones is
well suppressed. Here, a THz ( 560 GHz) wave with an unprecedented
phase noise is provided by a frequency-stabilized, dissipative Kerr
microresonator soliton comb. The repetition frequency of the comb is stabilized
to a long fiber in a two-wavelength delayed self-heterodyne interferometer,
significantly reducing the phase noise of the THz wave. A new measurement
technique to characterize the phase noise of the THz wave beyond the limit of a
frequency-multiplied microwave is also demonstrated, showing the superior phase
noise of the THz wave to any other THz oscillators (> 300 GHz)
Full-field fluorescence lifetime dual-comb microscopy using spectral mapping and frequency multiplexing of dual-comb optical beats
Fluorescence lifetime imaging microscopy (FLIM) is a powerful tool for quantitative fluorescence imaging because fluorescence lifetime is independent of concentration of fluorescent molecules or excitation/detection efficiency and is robust to photobleaching. However, since most FLIMs are based on point-to-point measurements, mechanical scanning of a focal spot is needed for forming an image, which hampers rapid imaging. Here, we demonstrate scan-less full-field FLIM based on a one-to-one correspondence between two-dimensional (2D) image pixels and frequency-multiplexed radio frequency (RF) signals. A vast number of dual-comb optical beats between dual optical frequency combs are effectively adopted for 2D spectral mapping and high-density frequency multiplexing in the RF region. Bimodal images of fluorescence amplitude and lifetime are obtained with high quantitativeness from amplitude and phase spectra of fluorescence RF comb modes without the need for mechanical scanning. The parallelized FLIM will be useful for rapid quantitative fluorescence imaging in life science
Scan-less full-field fluorescence-lifetime dual-comb microscopy using two-dimensional spectral mapping and frequency multiplexing of dual-optical-comb beats
Fluorescence lifetime imaging microscopy (FLIM) is a powerful tool for
quantitative fluorescence imaging because fluorescence lifetime is independent
of concentration of fluorescent molecules or excitation/detection efficiency
and is robust to photobleaching. However, since FLIM is based on point-to-point
measurements, mechanical scanning of a focal spot is needed for forming an
image, which hampers rapid imaging. In this article, we demonstrate scan-less
full-field FLIM based on a one-to-one correspondence between two-dimensional
(2D) image pixels and frequency-multiplexed RF signals. A vast number of
dual-optical-comb beats between dual optical frequency combs is effectively
adopted for 2D spectral mapping and high-density frequency multiplexing in
radio-frequency region. Bimodal images of fluorescence amplitude and lifetime
are obtained with high quantitativeness from amplitude and phase spectra of
fluorescence RF comb modes without the need for mechanical scanning. The
proposed method will be useful for rapid quantitative fluorescence imaging in
life science.Comment: 38 pages, 8 figures, 1 tabl
Optical image amplification in dualcomb microscopy
Dual-comb microscopy (DCM), based on a combination of dual-comb spectroscopy (DCS) with two-dimensional spectral encoding (2D-SE), is a promising method for scan-less confocal laser microscopy giving an amplitude and phase image contrast with the confocality. However, signal loss in a 2D-SE optical system hampers increase in image acquisition rate due to decreased signal-to-noise ratio. In this article, we demonstrated optical image amplification in DCM with an erbium-doped fiber amplifier (EDFA). Combined use of the image-encoded DCS interferogram and the EDFA benefits from not only the batch amplification of amplitude and phase images but also significant rejection of amplified spontaneous emission (ASE) background. Effectiveness of the optical-image-amplified DCM is highlighted in the single-shot quantitative nanometer-order surface topography and the real-time movie of polystyrene beads dynamics under water convection. The proposed method will be a powerful tool for real-time observation of surface topography and fast dynamic phenomena
Visualization of internal structure and internal stress in visibly opaque objects using full-field phase-shifting terahertz digital holography
We construct a full-field phase-shifting terahertz digital holography (PS-THz-DH) system by use of a THz quantum cascade laser and an uncooled, 2D micro-bolometer array. The PS-THz-DH enables us to separate the necessary diffraction-order image from unnecessary diffraction-order images without the need for spatial Fourier filtering, leading to suppress the decrease of spatial resolution. 3D shape of a visibly opaque object is visualized with a sub-millimeter lateral resolution and a sub-μm axial resolution. Also, the digital focusing of amplitude image enables the visualization of internal structure with the millimeter-order axial selectivity. Furthermore, the internal stress distribution of an externally compressed object is visualized from the phase image. The demonstrated results imply a possibility for non-destructive inspection of visibly opaque non-metal materials
Terahertz wireless communication at 560-GHz band using Kerr micro-resonator soliton comb
Terahertz (THz) waves have attracted attention as carrier waves for
next-generation wireless communications (6G). Electronic THz emitters are
widely used in current mobile communications; however, they may face technical
limitations in 6G with upper-frequency limits. We demonstrate wireless
communication in a 560-GHz band by using a photonic THz emitter based on
photomixing of a 560-GHz-spacing soliton microcomb in a uni-travelling carrier
photodiode together with a THz receiver of Schottky barrier diode. The on-off
keying data transfer with 2-Gbit/s achieves a Q-factor of 3.4, thus, satisfying
the limit of forward error correction.Comment: 17 pages, 4 figur